The present invention relates to optical communications, and more particularly to optical communication systems employing multiple wavelengths.
Wavelength division multiplexing (WDM) is a technique used to combine multiple optical signals having disparate wavelengths onto the same fiber. This technique has many advantages in implementing optical communication systems including increased capacity and the ability to use passive optical components to redirect a portion of the signal flowing along the fiber for processing at an intermediate node.
The trend in optical communication systems is toward greater numbers of wavelengths, narrower spacings between channels, higher data rate signals, and longer distance transmission without the use of repeaters. Along very long links, it is normally desirable to reroute, terminate, and/or insert wavelengths at intermediate points. Accordingly, it is typical to include optical add/drop multiplexers (OADMs) that are capable of removing and substituting selected wavelengths in the optical signal flowing through an intermediate point along the link. Such OADMs are often combined at the same line site with all-optical amplifiers such as Erbium-doped fiber amplifiers (EDFAs) and/or dispersion compensation units (DCUs).
The number of wavelengths to be removed and substituted and their spectral locations will be different for each line site. A difficulty then arises in that passive optical components of the OADM must then be specified differently for each line site, raising costs, and limiting operator flexibility in reconfiguring the network.
What is needed is increased configurability of OADMs to accommodate requirements of different line sites.
By virtue of one embodiment of the present invention, a partially configurable optical add/drop multiplexer (OADM) is provided. Fixed single channel and wideband tunable fiber Bragg gratings may be used in combination. OADM channel configuration may be changed by tuning one or more tunable fiber Bragg gratings.
A first aspect of the present invention provides apparatus for processing a multi-wavelength optical signal in a frequency-selective manner. The apparatus includes: a first optical notch filter that reflects optical energy at a first selected wavelength and passes other optical energy, a second optical notch filter that reflects optical energy at a second selected wavelength and passes other optical energy, and a tunable passband filter that reflects optical energy within a tunable passband and passes other optical energy, the tunable passband filter and the first and second optical notch filters being in cascade with another.
A second aspect of the present invention provides a method for processing a multi-wavelength optical signal in a frequency-selective manner. The method includes: directing the optical signal through a first optical notch filter that reflects optical energy at a first selected wavelength and passes other optical energy, directing the optical signal through a second optical notch filter that reflects optical energy at a second selected wavelength and passes other optical energy, and directing the optical signal through a tunable passband filter that reflects optical energy within a tunable passband and passes other optical energy. The tunable passband filter and the first and second optical notch filters are in cascade with another.